VO2 max is the maximum amount of oxygen your body can use during hard exercise, measured in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min). It is one of the best single markers of cardiorespiratory fitness, and here higher is better. As a rough guide, a healthy adult score is about 36 mL/kg/min or above for men and 30 mL/kg/min or above for women, though what counts as "normal" shifts with age, sex and training.
What is VO2 max?
VO2 max (maximal oxygen uptake) reflects how well your heart, lungs, blood and muscles work together to take in oxygen and deliver it to working tissue. Because almost every part of the cardiovascular and respiratory system contributes, it is widely used as a summary measure of aerobic fitness and overall cardiovascular health.
The gold-standard measurement is a graded exercise test in a lab, where you run or cycle to exhaustion while a mask analyses the oxygen and carbon dioxide in your breath. Most people, however, first meet the number on a smartwatch or fitness tracker, which estimates VO2 max from heart rate and pace during activity. These estimates are useful for tracking your own trend over time, but a single reading can be off by several points, so treat wearable numbers as a direction of travel rather than a precise lab value. VO2 max matters because a higher score is consistently linked with better exercise capacity, and because it responds to training — it is one of the most modifiable fitness markers you have. You can see how it fits alongside other heart and lung metrics on our Vitals & Imaging hub.
VO2 max normal range
There is no single "normal" VO2 max — it depends heavily on sex, age and fitness. Using the general adult reference bands below, a score in the normal tier means your cardiorespiratory fitness is in a healthy range, and anything higher is better still. The table shows the default adult severity bands in mL/kg/min.
| Fitness tier | VO2 max (mL/kg/min) |
|---|---|
| Normal (healthy) | 30 and above |
| Borderline low | 25 – 29.9 |
| Moderately low | 20 – 24.9 |
| Severely low | 15 – 19.9 |
| Critically low | 0 – 14.9 |
These bands follow ACSM Exercise Testing Guidelines. In Indian labs and clinics VO2 max is reported in the same mL/kg/min units, so results are directly comparable. If your only source is a wearable, remember it is estimating this figure — a reading that drifts up or down by a couple of points between weeks is usually noise, not a real change in fitness.
Normal range by age, sex or fitness
VO2 max is strongly shaped by sex and by training status, and it naturally declines with age. The table below shows the "normal" (healthy) threshold and the tiers below it for different groups, all in mL/kg/min, built from the ACSM reference rows.
| Group | Normal (healthy) | Borderline low | Moderately low | Severely low | Critically low |
|---|---|---|---|---|---|
| Adult male | 36 and above | 31.5 – 35.9 | 26.5 – 31.4 | 20 – 26.4 | 0 – 19.9 |
| Adult female | 30 and above | 25 – 29.9 | 21 – 24.9 | 15 – 20.9 | 0 – 14.9 |
| Athlete | 45 and above | 40 – 44.9 | 35 – 39.9 | 25 – 34.9 | 0 – 24.9 |
| Senior (65+) | 25 and above | 21 – 24.9 | 17 – 20.9 | 12 – 16.9 | 0 – 11.9 |
Adult men generally record higher VO2 max than women, largely because of differences in muscle mass and blood haemoglobin, so the healthy threshold sits higher at 36 mL/kg/min. Adult women have a healthy threshold around 30 mL/kg/min for the same reasons. Athletes and highly trained endurance individuals reach much higher values, so a fitness-appropriate "normal" only starts at about 45 mL/kg/min. Seniors aged 65 and over have lower expected values because VO2 max declines with age as maximum heart rate and muscle mass fall, so 25 mL/kg/min and above is considered healthy for this group. Compare your own group's threshold rather than a single universal number.
What a high VO2 max means
Because higher is better, a high VO2 max is a good thing: it signals strong cardiorespiratory fitness and a heart, lungs and muscles that deliver and use oxygen efficiently. Endurance athletes such as distance runners, cyclists and rowers typically sit well into or above the athlete band. A rising VO2 max over months usually reflects successful aerobic training. There is essentially no "too high" from a health standpoint — an unusually high value is a sign of excellent conditioning, not a problem. If a wearable suddenly reports a large jump, suspect a measurement quirk (a very fast run in cool weather, or a heart-rate glitch) before assuming your fitness leapt overnight; trends over weeks are more reliable than one flattering reading.
What a low VO2 max means
A VO2 max that falls into the borderline, moderate, severe or critical tiers points to reduced cardiorespiratory fitness. The most common cause is simply a sedentary lifestyle and deconditioning, which is very responsive to training. Other contributors include increasing age, being overweight (VO2 max is expressed per kilogram of body weight), smoking, and heart or lung conditions that limit oxygen delivery. A persistently low or falling score can be an early nudge to look at your activity levels and overall heart health, and lower cardiorespiratory fitness is broadly associated with higher cardiovascular risk — which is why fitness sits alongside markers like your ASCVD risk score in the bigger picture. A low estimate on a wearable alone is not a diagnosis; if it is genuinely low and paired with breathlessness on mild exertion, chest discomfort or unusual fatigue, that is worth raising with a doctor or cardiologist.
How to improve VO2 max and what to do
VO2 max is one of the most trainable fitness metrics. Evidence-aligned ways to raise it include:
- Do regular aerobic exercise — brisk walking, jogging, cycling or swimming most days builds the aerobic base that underpins VO2 max.
- Add interval training — alternating harder efforts with easier recovery is a particularly effective stimulus for improving maximal oxygen uptake.
- Build gradually and stay consistent — steady progression over weeks and months matters far more than any single hard session.
- Support it with lifestyle basics — not smoking, managing weight and sleeping well all help your heart and lungs work efficiently.
In India, everyday options such as walking or cycling to work, using stairs, and joining a local park run or gym make aerobic training accessible without special equipment. Warm, humid conditions and air quality can affect how a hard session feels, so pace yourself and hydrate. When to see a doctor: if your fitness is very low, dropping despite training, or accompanied by chest pain, marked breathlessness, palpitations or dizziness, talk to a doctor or cardiologist before pushing intensity. Tracking your fitness trends over time — something you can do with ExaHealth alongside your other vitals — helps you and your clinician see the direction, not just one number. It also pairs naturally with metrics like your resting heart rate and heart rate variability.
Guidelines and references
The reference bands in this article are based on published fitness testing standards:
- American College of Sports Medicine (ACSM) — Exercise Testing Guidelines and athletic performance standards: https://www.acsm.org
Frequently asked questions
What is a good VO2 max?
For general adults, a healthy VO2 max is about 30 mL/kg/min or above, with 36 and above the healthy threshold for men and 30 and above for women. Because higher is better, values in the athlete range (45+ mL/kg/min) reflect excellent fitness.
What is a normal VO2 max by age?
Normal VO2 max declines with age. Healthy thresholds are around 36 mL/kg/min for adult men and 30 for adult women, easing to about 25 mL/kg/min for people aged 65 and over, per ACSM reference ranges.
Is VO2 max higher or lower better?
Higher is better. VO2 max measures how much oxygen your body can use during hard exercise, so a higher number means stronger cardiorespiratory fitness. There is no meaningful "too high" from a health point of view.
Are smartwatch VO2 max readings accurate?
Consumer wearables estimate VO2 max from heart rate and pace rather than measuring it directly, so a single reading can be off by several points. Use the trend over weeks rather than one number, and confirm with a lab test if precision matters.
How can I improve my VO2 max?
Regular aerobic exercise plus interval training is the most effective approach, built up gradually and consistently over weeks. Not smoking, managing weight and sleeping well support the gains.
Does VO2 max differ between men and women?
Yes. Men generally record higher VO2 max than women, mainly due to differences in muscle mass and blood haemoglobin, so the healthy threshold is about 36 mL/kg/min for men versus 30 for women.